Noninvasive CPAP procedures have come into widespread use for the treatment of sleep apnea and during episodes of acute and chronic respiratory failure without using endrotracheal intubation. All forms of such non-invasive positive pressure ventilation (PPV) procedures require that a mask be worn over a respiratory orifice of a patient to provide an interface with a source of positive pressure. A leak port is provided on the mask to vent exhaled CO2 from the system. Current CPAP technology relies on a predetermined low pressure of greater than approximately 3-5 cm H2O to vent exhaled gas out of the leak port during exhalation. However, when a positive pressure supplied by a pressurized air source falls below this value, venting through the leak port ceases, thus causing a buildup of exhaled CO2 within the mask.